1). Field of the Invention
This invention relates to a method and device for improving cardiac function.
2). Discussion of Related Art
Congestive heart failure annually leads to millions of hospital visits internationally. Congestive heart failure is a description given to a myriad of symptoms that can be the result of the heart's inability to meet the body's demand for blood flow. In certain pathological conditions, the ventricles of the heart become ineffective in pumping the blood, causing a back-up of pressure in the vascular system behind the ventricle.
The reduced effectiveness of the heart is usually due to an enlargement of the heart. A myocardial ischaemia may, for example, cause a portion of a myocardium of the heart to lose its ability to contract. Prolonged ischemia can lead to infarction of a portion of the myocardium (heart muscle) wherein the heart muscle dies and becomes scar tissue. Once this tissue dies it no longer functions as a muscle and cannot contribute to the pumping action of the heart. When the heart tissue is no longer pumping effectively, that portion of the myocardium is said to be hypokinetic, meaning that it is less contractile than the uncompromised myocardial tissue. As this situation worsens, the local area of compromised myocardium may in fact bulge out as the heart contracts, further decreasing the heart's ability to move blood forward. When local wall motion moves in this way it is said to be dyskinetic. The dyskinetic portion of the myocardium may stretch and eventually form an aneurysmic bulge. Certain diseases may cause a global dilated myopathy, i.e., a general enlargement of the heart when this situation continues for an extended period of time. As the heart begins to fail, the filling pressures increase, which stretches the ventricular chamber prior to contraction, greatly increasing the pressure (preload) to the heart. In response, the heart tissue remodels to accommodate the chronically increased filling pressures, further increasing the work that the now-compromised myocardium must perform. This vicious cycle of cardiac failure results in the symptoms of congestive heart failure such as shortness of breath on exertion, edema in the periphery, nocturnal dypsnia (a characteristic shortness of breath that occurs at night after going to bed), weight gain, and fatigue, to name a few. The enlargements increase stress on the myocardium. The stress increase requires a larger amount of oxygen supply, which can result in exhaustion of the myocardium leading to a reduced cardiac output of the heart.